The invention relates to disc drive storage systems using accelerometers that are manufactured as micro-electro-mechanical systems (MEMS). In particular, the invention relates to the in-situ testing of MEMS accelerometers for use with disc drives.
Accelerometers are used in conjunction with disc drives to provide real time data for various control systems associated with the disc drive.
In U.S. Pat. No. 5,521,772 Lee et al., for example, an acceleration rate sensor is mounted on a disc drive housing and used to inhibit writing to the disc when the disc drive is subjected to external shock or vibration. In U.S. Pat. No. 5,856,895 Schaenzer et al., an accelerometer is integrally formed in a slider of a disc drive and its output is used to improve servo performance in the disc drive.
Accelerometers can be manufactured using MEMS technology, however, such MEMS accelerometers are extremely small, delicate and subject to damage from electrical or mechanical overstresses. MEMS technology uses microstructure fabrication techniques that are adapted from integrated circuit manufacture such as photolithographic masking, etching, vapor deposition, ion implantation and the like. The extremely small size and mass of MEMS accelerometers makes them especially useful in high performance applications such as disc drive systems. In such systems, there is a desire to diagnose accelerometer failure, without disassembling the accelerometer for inspection. The installation of a second accelerometer merely to test a first MEMS accelerometer would add to the mass, cost and complexity of the system. The artificial application of a known, calibrated acceleration force to test the accelerometer would be cost prohibitive.
A method and an apparatus are needed to test a MEMS accelerometer in a disc storage system without disassembling the MEMS accelerometer and without the undesirable addition of a second accelerometer for comparison, and without the artificial application of an acceleration force to the disc drive.
Disclosed is a method and circuit performing a self test on a MEMS accelerometer associates with a disc drive. The MEMS accelerometer includes a self test input that establishes a self test condition in the MEMS accelerometer during a self test interval. The circuit also includes a stored reference representing at least one characteristic limit of an integrity output of the MEMS accelerometer. The circuit also includes a test circuit that is adapted to receive at least one integrity output value and the stored reference during the self test interval and that generates a self test output representative of integrity of the MEMS accelerometer.
Degraded integrity or damage to a MEMS accelerometers can be diagnosed in-situ. Mounting of a second accelerometer or other sensors for diagnosis can be avoided. Disassembly of the MEMS accelerometer for diagnosis can also avoided. Artificial application of an acceleration force to the disc drive can also be avoided.
In a preferred embodiment, the MEMS accelerometer is a capacitive accelerometer that senses rotational vibration and that is mounted on the associated disc drive.